Extraction with sulphur dioxide



H. H. M EiER June 18, 1946.

EXTRACTION WITH SULPHUR DIOXIDE Filed Sept. 14, 1942 hozo z zz a uEL oHg 34 INVENTOR.

29:95am W m Ehovohv I 5:200 k IIEQ Patented June 18, 1946 EXTRACTION WITH SULPHUR DIOXIDE Herbert H. Meier, Baytown, Tex., assignor to Standard Oil Develo ration of Delaware pment Company, a corpo- Application September 14, 1942, Serial No. 458,310

The present; invention is directed to the- S02 extraction of petroleum fractions containing olefins.

The extraction of petroleum fractions with S02 is a well known procedure in refinery operations. For the most part, it has been practiced on a commercial basis on virgin distillates. Attempts to apply it to cracked distillates have led to operating difiiculties, such as coking of heat exchangers and of other equipment which is heated in the course of the operation to separate S02 from the extract and the raflinate. This trouble has been particularly pronounced in operations in which hydroformed naphthas have been employed as the feed stock for the extraction.

It has now been found that these coking troubles hitherto experienced in heated equipment utilized in the handling of mixtures of S02 and petroleum fractions containing olefins can be avoided if care is taken to eliminate oxygen other than that combined with the S02 from the mixtures. This exclusion of oxygen should be observed at least from the time the petroleum fraction comes into contact with the $02 until the two are separated. To this end, the petroleum fraction should be treated just before being mixed with the $02 to remove from it any free oxygen 3 Claims. (01. 196-37) or organic peroxides which may be contained in it. In suitable cases this can be done by a stripping operation in which the oxygen is taken off overhead and the organic peroxides are rejected as bottoms. Immediately following this operation, the fraction is blanketed with an inert gas, such as methane, nitrogen, etc., until it is mixed with the $02. The system from this point on is ordinarily a closed system, but if there are any accumulators or storage tanks in the system while the petroleum fraction and the S02 are in contact with each other, these also must be blanketed with the inert gas or kept under pressure to exclude air or oxygen.

In practice, however, it is preferable to go further and protect the petroleum fraction from contamination with oxygen from the very moment the olefins are formed in the fraction. That is to say, immediately after the cracking, hydroforming, or other thermal treatment, with or without catalysts, which converts parafiins into olefins, the petroleum fraction is subjected to a distillation to remove any free oxy en that may be present therein and then put in storage under an inert gas until ready for extraction with S02. In this way contact between the petroleum fraction and oxygen for a length of time sufficient The manner in which the present invention is practiced may be better understood from the following detailed description of the accompanying drawing in which the single figure is a front elevation, in diagrammatic form, of one type of apparatus suitable for such practice.

Referring to the drawing in detail, numeral l designates a feed line for feeding petroleum distillate into a processing unit 2 which may be a cracking unit or a hydroforming unit or a cyclization unit or any other type of processing unit in which hydrogen is split off from the hydrocarbons. The efiiuent from this unit isoonducted, by line 3, into a distillation column 4, from which the light ends are taken of! overhead by. line 5. It will be understood that this represents the preferred type of operation in which any oxygen contained in the distillate is taken off overhead with the light ends. The remainder is conducted by line 6 into a second distillation column 1 in which the desired cut for S02 extraction is taken on overhead by line 8 and discharged into a storage tank 9, which is supplied with a feed line it for inert gas and a pressure relief line I i containing, if desired, a safety valve. It may be observed that an extremely slow stream of the inert gas may be maintained through the storage tank, since its purpose is merely to exclude oxygen or air.

The petroleum fraction is then withdrawn from the storage tank through line l2 and introduced into an S02 extraction'unit l3 into the upper end of which is fed S02 through line It, and from the top of which a raflinate is recovered through line [5 and from the bottom of which an extract is drawn ofi through line 6. It is in the further treatment of this extract to separate the S02 from the hydrocarbons by operations which involve heating steps that coking of the equipment subjected to elevated temperatures has previously been experienced. For example, in one such unitthe heat exchangers and other heated recovery equipment in which the extract in line It was processed coked so rapidly that it was necessary to shut it down after operating for only a 6-day period and to resort to extensive cleaning of it, which involved a 6-day down time. It was found that in most parts of the equipment which were subjected to high temperatures there was a hard coke-like deposit, the removal of which was extremely difiicult. After the'blanketing operation described above was adopted, the same equipment was operated continuously for a 54-day period, after which a thorough investigation revealed for the formation of organic peroxides is avoided. that coke deposition had been negligible. In this 3 particular case, the hydrocarbon feed stock to the extraction unit was a hydroformed naphtha cut boiling between about 200 and 250 F.

The nature and objects of the present invention having been thus described and illustrated,

what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. In a method in which a petroleum naphtha is subjected to a thermal conversion and then to extraction with sulphur dioxide, the steps of eliminating from said naphtha immediately after said conversion any organic peroxides and oxygen contained therein, and thereafter excluding oxygen from any atmosphere with which said naphtha may come into contact until the extraction with sulphur dioxide has been completed.

2. In a method in which a petroleum distillate containing olefins is extracted with sulphur dioxide, the steps of preliminarily removing from said distillate any oxygen contained therein,

then blanketing said distillate with an inert gas until the extraction has begun, and excluding organic peroxides and oxygen from any atmosphere with which the mixture of distillate and sulphur dioxide comes into, contact until the extraction is completed and the sulphur dioxide has been separated from said distillate.

3. In a method in which a petroleum naphtha is subjected to a thermal conversion which produces olefins in the naphtha, and subsequently to an extraction with sulphur dioxide, the steps of removing organic peroxides an oxygen from said naphtha immediately after said conversion, and thereafter blanketing said naphtha, whenever there is a free space above it, with an inert gas until the extraction with sulphur dioxide is comi pleted and the sulphur dioxide is separatedfrom the naphtha.

HERBERT H. MEIER. 

